I'd like to suggest an approach for handling material that
differs between the show and the book (or that is expanded upon in
the book). The best approach I have seen comes from the Game of
Thrones wiki, which uses the TV show as its chief point of
reference. Then, where appropriate, it adds material from the
books, in a section in each article generally called "In the
books." (Here's an example.)

I think this is a smart way of doing things, and I think we
should follow it here. Most folks who visit this wiki will do so
out of interest in the show, so that's our obvious focal point. But
where it's helpful, we should include information from the book. As
an example, I've preliminarily done so on the page for The
Grasshopper Lies Heavy.